US7778384B2 - Direct measuring and correction of scatter for CT - Google Patents

Direct measuring and correction of scatter for CT Download PDF

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Publication number
US7778384B2
US7778384B2 US12/065,614 US6561406A US7778384B2 US 7778384 B2 US7778384 B2 US 7778384B2 US 6561406 A US6561406 A US 6561406A US 7778384 B2 US7778384 B2 US 7778384B2
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scatter
data
radiation
image data
focal spot
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US20080226020A1 (en
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Roland Proksa
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Koninklijke Philips NV
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Koninklijke Philips Electronics NV
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/03—Computed tomography [CT]
    • A61B6/032—Transmission computed tomography [CT]
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/40—Arrangements for generating radiation specially adapted for radiation diagnosis
    • A61B6/4021—Arrangements for generating radiation specially adapted for radiation diagnosis involving movement of the focal spot
    • A61B6/4028—Arrangements for generating radiation specially adapted for radiation diagnosis involving movement of the focal spot resulting in acquisition of views from substantially different positions, e.g. EBCT
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
    • A61B6/5258—Devices using data or image processing specially adapted for radiation diagnosis involving detection or reduction of artifacts or noise
    • A61B6/5282—Devices using data or image processing specially adapted for radiation diagnosis involving detection or reduction of artifacts or noise due to scatter
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/027—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/42—Arrangements for detecting radiation specially adapted for radiation diagnosis
    • A61B6/4291—Arrangements for detecting radiation specially adapted for radiation diagnosis the detector being combined with a grid or grating

Definitions

  • the invention relates to the field of tomographic imaging.
  • the invention relates to an examination apparatus for examination of an object of interest, to an image processing device, to a method of examination of an object of interest, a computer-readable medium and a program element.
  • Cone-beam CT scanners with large detector arrays suffer from increased scatter radiation. This radiation may cause severe image artefacts.
  • two-dimensional anti-scatter-grids (ASG) may be used.
  • ASG two-dimensional anti-scatter-grids
  • conventional two-dimensional anti-scatter-grids may not allow for advanced CT system concepts such as the so-called stereo-tube design.
  • an examination apparatus for examination of an object of interest comprising a radiation source adapted for emitting electromagnetic radiation to the object of interest, a detector unit adapted for detecting image data and scatter data from the object of interest, and a correction unit adapted for correcting the image data on the basis of the scatter data, wherein the image data is detected at a first position of a focal spot of the electromagnetic radiation relative to the detector unit, and wherein the scatter data is detected at a second position of the focal spot relative to the detector unit, wherein the second position is different from the first position.
  • scatter data may be acquired when the focal spot has been moved relative to the detector unit to a second position which is different from the (normal) first position of the focal spot (at which the image data is acquired).
  • two different data sets may be acquired, mainly the image data and (at a different position of the focal spot) the scatter data. This scatter data is then used for image correction.
  • the examination apparatus further comprises an anti-scatter-grid adapted for filtering the electromagnetic radiation.
  • the anti-scatter-grid may be adapted such that no direct radiation hits the detector unit when the electromagnetic radiation is focussed to the second position of the focal spot.
  • the scatter data which is detected from the detector unit may comprise only little or even none direct radiation data.
  • the anti-scatter-grid is a 1-dimensional anti-scatter-grid.
  • This may provide for an easy fabrication of the ASG. Furthermore, this may allow for the application for advanced CT system concepts such as stereo-tube design.
  • the image data comprises a first amount of direct radiation and a second amount of scatter radiation.
  • the scatter data comprises a third amount of direct radiation and a fourth amount of scatter radiation.
  • a first fraction of the first amount and the second amount is significantly bigger than a second fraction of the third amount and the fourth amount.
  • the scatter data may only comprise a relatively small amount of direct radiation (which has not been scattered by the object of interest).
  • the amount of direct radiation reaching the detector may be significantly reduced. Therefore, the resulting measurement (scatter data) may basically only contain scattered photons. Such a measurement may provide a good estimation of the scatter contribution to the imaging measurements.
  • the radiation source is adapted for electronically moving the focal spot from the first position to the second position.
  • the image data is detected at a first time and the scatter data is detected at a second time, wherein the first time and the second time correspond to a detection sequence.
  • a detection sequence may be pre-determined. Then, during data acquisition, the focal spot is switched between the first position and the second position (for acquisition of image data and scatter data, respectively) according to the pre-determined detection or switching sequence. Since scatter may vary slowly in the spatial domain, the scatter measurements may only sporadically be interleaved in the image acquisition (according to the pre-determined detection sequence).
  • the correction unit is further adapted for performing a first interpolation to substitute a missing imaging projection.
  • the correction unit is further adapted for performing a second angular interpolation to generate a scatter estimate for each projection angle.
  • the examination apparatus is further adapted for performing a low-pass filtering of the scatter data.
  • the examination apparatus may be applied as a baggage inspection apparatus, a medical application apparatus, a material testing apparatus or a material science analysis apparatus.
  • a field of application of the invention may be material science analysis, since the defined functionality of the invention may allow for a secure, reliable and highly accurate analysis of a material.
  • the examination apparatus may further comprise a collimator arranged between the electromagnetic radiation source and the detector unit, wherein the collimator is adapted for collimating an electromagnetic radiation beam emitted by the electromagnetic radiation source to form a cone-beam.
  • the radiation source may be adapted for emitting a polychromatic radiation beam.
  • an image processing device for examination of an object of interest comprising a memory for storing image data and scatter data of the object of interest.
  • the image processing device may comprise a correction unit adapted for correcting the image data on the basis of the scatter data, wherein the image data is detected at a first position of a focal spot of the electromagnetic radiation relative to the detector unit, and wherein the scatter data is detected at a second position of the focal spot relative to the detector unit, wherein the second position is different from the first position.
  • an image processing device may be provided which is adapted for performing an improved scatter correction for, for example, a cone-beam computer tomography apparatus.
  • a method of examination of an object of interest comprising the steps of emitting electromagnetic radiation to the object of interest, detecting image data and scatter data of the object of interest, and correcting the image data on the basis of the scatter data.
  • the image data is detected at a first position of a focal spot of the electromagnetic radiation relative to the detector unit and the scatter data is detected at a second, different position of the focal spot relative to the detector unit.
  • a computer-readable medium in which a computer program of examination of an object of interest is stored which, when being executed by a processor, is adapted to carry out the above-mentioned method steps.
  • the present invention relates to a program element of examination of an object of interest, which may be stored on the computer-readable medium.
  • the program element may be adapted to carry out the steps of emitting electromagnetic radiation to the object of interest, detecting image data and scatter data of the object of interest and correcting the image data on the basis of the scatter data.
  • the program element may preferably be loaded into working memories of a data processor.
  • the data processor may thus be equipped to carry out exemplary embodiments of the methods of the present invention.
  • the computer program may be written in any suitable programming language, such as, for example, C++ and may be stored on a computer-readable medium, such as a CD-ROM. Also, the computer program may be available from a network, such as the WorldWideWeb, from which it may be downloaded into image processing units or processors, or any suitable computers.
  • the scatter radiation measurement may be performed by utilizing a 1-dimensional anti-scatter-grid and an X-ray tube with an electronic focal spot movement. This may provide for an improved scatter correction and may lead to an improved image quality.
  • FIG. 1 shows a simplified schematic representation of an examination apparatus according to an exemplary embodiment of the present invention.
  • FIG. 2 shows a flow-chart of an exemplary method according to the present invention.
  • FIG. 3 shows an exemplary embodiment of an image processing device according to the present invention, for executing an exemplary embodiment of a method in accordance with the present invention.
  • FIG. 1 shows an examination apparatus according to an exemplary embodiment of the present invention which is adapted as a computer tomography apparatus.
  • the present invention will be described for the application in medical imaging.
  • the present invention is not limited to this application, but may also be applied in the field of baggage inspection, or other industrial applications, such as material testing.
  • the computer tomography apparatus 100 depicted in FIG. 1 is a cone-beam CT scanner.
  • the CT scanner depicted in FIG. 1 comprises a gantry 101 , which is rotatable around a rotational axis 102 .
  • the gantry 101 is driven by means of a motor 103 .
  • Reference numeral 104 designates a source of radiation such as an X-ray source, which, according to an aspect of the present invention, emits a polychromatic radiation.
  • Reference numeral 105 designates an aperture system which forms the radiation beam emitted from the radiation source to a cone-shaped radiation beam 106 .
  • the cone-beam 106 is directed such that it penetrates an object of interest 107 arranged in the centre of the gantry 101 , i.e. in an examination region of the CT scanner, and impinges onto the detector 108 .
  • the detector 108 is arranged on the gantry 101 opposite to the source of radiation 104 , such that the surface of the detector 108 is covered by the cone-beam 106 .
  • the detector 108 which is depicted in FIG. 1 , comprises a plurality of detector elements 123 each capable of detecting, in an energy-resolving manner, X-rays or individual photons which have penetrated the object of interest 107 .
  • the source of radiation 104 , the aperture system 105 and the detector 108 are rotated along the gantry 101 in the direction indicated by arrow 116 .
  • the motor 103 is connected to a motor control unit 117 , which is connected to a calculation or correction unit 118 .
  • the object of interest 107 may be a patient or an item of baggage which is disposed on a conveyor belt 119 .
  • the conveyor belt 119 displaces the object of interest 107 along a direction parallel to the rotational axis 102 of the gantry 101 .
  • the conveyor belt 119 may also be stopped during the scans to thereby measure single slices.
  • a movable table may be used instead of providing a conveyor belt 119 .
  • the detector 108 may be connected to the calculation or correction unit 118 .
  • the correction unit 118 may receive the detection result, i.e. the read-outs from the detector elements 123 of the detector 108 and may determine a scanning result on the basis of the read-outs. Furthermore, the correction unit 118 communicates with the motor control unit 117 in order to coordinate the movement of the gantry 101 with motors 103 and 120 with the conveyor belt 119 .
  • the correction unit 118 may be adapted for correcting image data on the basis of scatter data, wherein the image data is detected at a first position 150 of a focal spot of the electromagnetic radiation relative to the detector unit 108 and wherein the scatter data is detected at a second position 151 of the focal spot relative to the detector unit 108 which is different from the first position, according to an exemplary embodiment of the present invention.
  • a reconstructed image generated by the correction unit 118 may be output to a display (not shown in FIG. 1 ) via an interface 122 .
  • the correction unit 118 may be realized by a data processor to process read-outs from the detector elements 123 of the detector 108 .
  • the correction unit 118 may be connected to a loudspeaker 121 , for example, to automatically output an alarm in case of the detection of suspicious material in the item of baggage 107 .
  • the computer tomography apparatus 100 for examination of the object of interest 107 includes the detector 108 having the plurality of detecting elements 123 arranged in a matrix-like manner, each being adapted to detect X-rays. Furthermore, the computer tomography apparatus 100 comprises the determination unit or reconstruction unit 118 adapted for reconstructing an image of the object of interest 107 .
  • the computer tomography apparatus 100 comprises the X-ray source 104 adapted to emit X-rays to the object of interest 107 .
  • the collimator 105 provided between the electromagnetic radiation source 104 and the detecting elements 123 is adapted to collimate an electromagnetic radiation beam emitted from the electromagnetic radiation source 104 to form a cone-beam.
  • the detecting elements 123 form a multi-slice detector array 108 .
  • the computer tomography apparatus 100 may be configured as a medical imaging apparatus or baggage inspection apparatus.
  • FIG. 2 shows a flow-chart of an exemplary method according to the present invention for directly measuring the scatter radiation and for using this measurement for a correction of the contaminated image data.
  • the method starts at step 1 with the emission of electromagnetic radiation by a radiation source to the object of interest. Furthermore, a conventional CT scan is performed. Then, in step 2 , the conventional data acquisition is interleaved with a scatter measurement by moving the focal spot such that no direct radiation hits the detector unit.
  • the measuring of scatter data is performed by utilizing, for example, 1-dimensional anti-scatter-grid 153 and an X-ray tube with an electronic focal spot movement.
  • the conventional 1-dimensional anti-scatter-grid 153 may have anti-scatter-lamella along the Z-direction to reduce the scatter in the fan direction.
  • the focal spot may be moved for a scatter measurement such that no or only little direct radiation hits the detector.
  • the resulting measurements may only contain scattered photons. Such a measurement may provide a good estimation of the scatter contribution to the imaging measurements.
  • step 3 an interpolation may be performed in order to substitute the missing imaging projections. Furthermore, in step 4 , an angular interpolation may be performed in order to generate a scatter estimate for each projection angle. Then, in step 5 , a low-pass filtering may be performed on the scatter measurements.
  • the image data may be corrected on the basis of the scatter data by a correction unit.
  • This correction may be performed by subtracting the scatter measurements from the imaging measurements to generate a corrected projection.
  • a reconstruction may be performed with the corrected projections, resulting in a corrected image of the object of interest.
  • the invention makes use of the fact that scatter radiation may usually have only very small spatial variations. A relative small movement of the focal spot for a scatter measurement may have very little impact on the scatter compared to the imaging measurements. Therefore, the imaging measurements may be interleaved with scatter measurements. Since scatter may very slowly in the spatial domain, the scatter measurements may sporadically be interleaved in the image acquisition (for example according to a pre-determined sequence.
  • FIG. 3 depicts an exemplary embodiment of a data processing device 400 according to the present invention for executing an exemplary embodiment of a method in accordance with the present invention.
  • the data processing device 400 depicted in FIG. 3 comprises a central processing unit (CPU) or image processor 401 connected to a memory 402 for storing an image depicting an object of interest, such as a patient or an item of baggage.
  • the data processor 401 may be connected to a plurality of input/output network or diagnosis devices, such as a CT device.
  • the data processor 401 may furthermore be connected to a display device 403 , for example, a computer monitor, for displaying information or an image computed or adapted in the data processor 401 .
  • An operator or user may interact with the data processor 401 via a keyboard 404 and/or other output devices, which are not depicted in FIG. 3 .
  • the bus system 405 it may also be possible to connect the image processing and control processor 401 to, for example, a motion monitor, which monitors a motion of the object of interest.
  • a motion monitor which monitors a motion of the object of interest.
  • the motion sensor may be an exhalation sensor.
  • the motion sensor may be an electrocardiogram.
  • Exemplary embodiments of the invention may be sold as a software option to CT scanner console, imaging workstations or PACS workstations.

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EP05108406.9 2005-09-13
EP05108406 2005-09-13
EP05108406 2005-09-13
PCT/IB2006/053054 WO2007031898A1 (en) 2005-09-13 2006-09-01 Direct measuring and correction of scatter for ct

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US20100208964A1 (en) * 2007-06-29 2010-08-19 Koninklijke Philips Electronics N.V. Method for eliminating scatter artefacts
US20120250968A1 (en) * 2011-03-31 2012-10-04 Siemens Aktiengesellschaft Method for generating image data of an object under examination, projection data processing device, x-ray system and computer program
CN104181177A (zh) * 2013-05-24 2014-12-03 上海联影医疗科技有限公司 Ct检测器位置校正方法
US20160199019A1 (en) * 2015-01-13 2016-07-14 Arineta Ltd. Method and apparatus for focal spot position tracking
US20180132807A1 (en) * 2016-11-07 2018-05-17 Shenzhen Institutes Of Advanced Technology Method and apparatus for optimizing blocking grating for cone beam ct image scattering correction

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DE102007052448A1 (de) * 2007-11-02 2009-05-07 Siemens Ag Korrektur der Querstreuung in einem Mehrstrahler-CT-Gerät
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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20100208964A1 (en) * 2007-06-29 2010-08-19 Koninklijke Philips Electronics N.V. Method for eliminating scatter artefacts
US20120250968A1 (en) * 2011-03-31 2012-10-04 Siemens Aktiengesellschaft Method for generating image data of an object under examination, projection data processing device, x-ray system and computer program
US8644577B2 (en) * 2011-03-31 2014-02-04 Siemens Aktiengesellschaft Method for generating image data of an object under examination, projection data processing device, X-ray system and computer program
CN104181177A (zh) * 2013-05-24 2014-12-03 上海联影医疗科技有限公司 Ct检测器位置校正方法
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WO2007031898A1 (en) 2007-03-22
JP2009507544A (ja) 2009-02-26
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